Extracellular recordings were made from VTA using a data acquisition system (DigiLynx, Neuralynx). VTA recording sites were verified histologically. The identity of dopaminergic cells was confirmed by recording the electrophysiological responses of cells to a brief blue light pulse train, which stimulates only DAT-expressing cells. Spikes were sorted using Spike-Sort3D (Neuralynx) or MClust-3.5 (A.D. Redish). Putative GABAergic neurons in the VTA were identified by clustering of firing patterns as described previously34 (link),37 (link). All confidence intervals are standard error unless otherwise noted.
Data analyses were performed using NumPy 1.15 and MATLAB R2018a (Mathworks). Spike times were collected in 1 ms bins to create peri-stimulus time histograms. These histograms were then smoothed by convolving with the function
where T was a time constant, set to 20 ms as in Eshel et al.34 (link). For single-cell traces, we set T to 200 ms for display purposes.
After smoothing, the data were baseline-corrected by subtracting from each trial and each neuron independently the mean over that trial’s activity from −1000 to 0 ms relative to stimulus onset (or relative to reward onset in the unexpected reward condition).
Data analyses were performed using NumPy 1.15 and MATLAB R2018a (Mathworks). Spike times were collected in 1 ms bins to create peri-stimulus time histograms. These histograms were then smoothed by convolving with the function
where T was a time constant, set to 20 ms as in Eshel et al.34 (link). For single-cell traces, we set T to 200 ms for display purposes.
After smoothing, the data were baseline-corrected by subtracting from each trial and each neuron independently the mean over that trial’s activity from −1000 to 0 ms relative to stimulus onset (or relative to reward onset in the unexpected reward condition).